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Title: Integration of high-K oxides with wide band-gap semiconductors
Authors: CHEN QIAN
Keywords: high-k, wide band-gap semiconductors, band alignment, MOSFET, XPS, interface
Issue Date: 6-Jan-2011
Citation: CHEN QIAN (2011-01-06). Integration of high-K oxides with wide band-gap semiconductors. ScholarBank@NUS Repository.
Abstract: Silicon-based Metal-oxide-semiconductor field effect transistors (MOSFET) devices have been thrust of research over the years and are the most developed. However, recent development has allowed silicon system technology to approach the theoretical limits, such as higher blocking voltage, switching frequency and large gate leakage current. To overcome these limitations, during the past several years, a new group of materials has emerged as candidates to replace silicon in the near future, which has enabled applications from optoelectronics devices to high-power, high-temperature, and high-frequency microelectronic devices. This group is known as the wide band-gap semiconductors (WBGs), and is led by SiC, ZnO and GaN. These large band-gap materials allow commercialization in power MOSFET devices, where Si cannot be used. Besides the recent progress of wide band-gap semiconductor to replace silicon in MOSFET devices, high-k oxides have been proposed as alternatives to replace conventional silicon dioxide in MOS devices. It is clear that the dielectric layer downscaling in MOSFET device is limited by the leakage current problem and it is an urgent task to introduce new dielectric material with higher dielectric constant (high-k) to replace silicon dioxide as the gate dielectrics. Therefore, in this thesis, integration of high-k dielectric materials with wide band-gap semiconductors was studied by using both experimental and theoretical methods. The growth and characterization (e.g. electronic structure, thermal stability) of HfO2 films on various wide band-gap semiconductor substrates (SiC, GaN and ZnO) were studied by in situ x-ray photoelectron spectroscopy (XPS). The band alignment at the HfO2/WBGs interface was accurately measured by XPS using a core-level based method. The sufficiently large band offsets between HfO2 films and various wide band-gap semiconductor substrates (SiC, GaN and ZnO) indicate that HfO2 dielectric is a promising candidate to be integrated with various wide band-gap semiconductors in the downscaling of MOSFET devices. The effects of interfacial structure on the band alignments and thermal stabilities of HfO2 films on SiC, GaN and ZnO substrates were also studied. It was found that the interfacial layer changed the band alignments by modifying the interfacial dipoles, which indicates that it is essential to understand and control the interfacial structure to improve the device performance. Ni was chosen as a prototype of metal gates to be grown on HfO2 to fabricate the Ni/HfO2/WBGs MOS capacitors. The capacitance and current properties responding to the variation of bias voltage of Ni/HfO2/WBGs MOS gate stacks in comparison with these of gate stacks after rapid thermal process (RTP) in nitrogen and oxygen ambient was investigated. It can be seen that the RTP can effectively reduce oxygen vacancies in the as-deposited HfO2 films. As a result, interface quality of HfO2/WBGs after RTP was improved. The effect of nitridation on the electronic structures and thermal stabilities of high-k dielectrics films (HfO2) was studied by using in situ x-ray photoelectron spectroscopy (XPS) and First-principles calculations. It was found that nitrogen doping not only can passivate the oxygen vacancies in high-k dielectrics films, but also can change the electronic structure of high-k dielectric films. This work suggests that the nitridation process should be well-controlled to optimize the performance of high-k dielectric films. The research of such integration of high dielectric oxide films on wide band-gap semiconductors by the combination of experimental and theoretical methods is very important not only for the fundamental research, but also in the field of semiconductor nanoelectronics device manufacture.
Appears in Collections:Ph.D Theses (Open)

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